Laminated tube



y 194% J. F. LEVAN 2,208,9S8

LAMINATED TUBE Filed July 28, 19338 y INVZIN 113R M BY M WWWZ A 7TORNEYS.

Patented July 23,1940 8 2,208,988

UNITED STATES! PATENT OFFlCE Curtain Company, Elkhart, Ind., acorporation of Indiana Application July 28, 1938, Serial No. 221,777

1 Claim. (Cl. 138-454) This invention relates to tubes used primarilyare substantially coextensive with each other. for rails, hand-holds,uprights, tubular framing Their margins on one side of the line ofdivision for different articles, as for cots, chairs, seats, of saidstrips are folded reversely and nested to etc., or in any situationwhere a tube with an form a hook-shaped loop at 5 and the other mar- 5outer, smooth, polished or lustrous surface is degins of said strips arefolded and nested together sired, or to tubes of the type shown in mypendto form a hook-shaped loop 6. The two loops are ing application,Serial No. 187,030, filed Januhooked together to form a lock seam jointconary 26, 1938, and has for its object the formation sisting of layersof stainless steel and the steel of a particularly strong rigid lockseam joint beof softer, tougher metal. The first layer, toward m tweenthe edges of an outer veneer strip of a finthe center of the tube, beingof the softer,

ishing metal, as stainless. steel, which joint is tougher' metal. Whenso folded and hooked tosnugly wedged in the slot of an internal bodygether, the lock seam joint is located in the slot tube and strengthenedby internal corrugations of the body I, and as seen in Figure 4, bulgesinto or internal knurling which so additionally inthe interior of thebody 1 beyond the inner surterlocks the laminations of the lock seamjoint, face thereof, before the tube is completely formed 15 as to makethe joint a substantially rigid rod to into the form shown in Figure 1.Then the resist torsional distortion. joint so consisting of laminationsis provided The corrugation or knurling feature is shown with transversecorrugations 1, these being as applied to the tube of my pendingapplicaformed by a knurling operation with a tool tion referred to.applied to the innermost lamination within the 20 Theinvention also hasfor its object the method tube, so that the corrugations or knurling areof forming the tube with the corrugated or exposed on the interior ofthe tube and the out-' knurled joint. side of the tube is smooth. Thecorrugations, as

The invention consists in the novel features seen in Figure 3, become ofless depth and greater and in the combinations and constructions andwidth from the interior of the tube toward the 25 in the methodhereinafter set forth and claimed. outer surface, and there arepractically no cor- Indescribing this invention, reference is hadrugations in the outer surface of the stainless to the accompanyingdrawing in which like charsteel tube 2 adjacent the edge 8 of the joint.

acters designate corresponding parts in all the The corrugating orknurling operation comviews. presses the joint and wedges it tightly inthe slot 30 Figure 1 is a fragmentary isometric view, on an and alsocloses up the joint at 8 to the smallest enlarged scale, of a tubingembodying this inpossible crevice. The joint thus formed, and byvention. reason of the corrugations, is particularly strong Figure 2 isa similar view but showing the to resist torsional strains applied tothe tube, outside of the joint, after being finished. without weldingand the consequent slight dis- Figure 3 is a longitudinal sectional viewon coloration of the stainless steel, due to the heat line 3--3,Figure 1. of the welding, and additional operations to Figure 4 is afragmentary sectional view eliminate such discoloration. through thejoint prior to being corrugated or The method consists in performing thecorruknurled. gating or knurling operation, after the tube has 40 Thetube here illustrated comprises an inner been formed up into the formshown in Figure 4, tubular body I, an outer veneer strip 2 of a metal,the knurling to be applied to the inner face of the as stainless steel,capable of receiving and mainjoint while pressure is applied to theouter face taining a high lustrous finish, and a reinforcing of thejoint, causing the joint to be flattened and strip 3 for the veneerstrip, this being of a softer, the laminations thereof interlocked bythe cortougher metal than the veneer strip. The outer rugations. Thetube is formed by passing two 45 strip 2 and the intermediate strip 3are coextenflat strips which form the layers 2, 3, flatwise on sive andhave their margins nested together by each other through rollers or dieswhich partly a lock seam joint. form them with marginal nested flangeswhich The body I may be of any suitable thickness of eventually areinterlocked and form the lock relatively cheap metal, and is divided orslotted seam joint in the finished article. After the longitudinallywith the edges 4 on opposite sides marginal flange forming operation, aflat strip of the division or slot spaced apart to provide a which formsthe backing I is fed flatwise onto the recess for the lock seam joint.two strips between the marginal flanges. Then The strips 2, 3 aredivided longitudinally and the three strips lying flatwise on each otherare fed through a series of dies or rollers which roll them up intotubular form and interlock the lock seam flanges of the layers 2, 3between the edges of the body I. After this operation, the tube is inthe form shown in Figure 4, and then the corrugating or knurlingoperation is performed which flattens the lock seam joint into theposition shown in Figure 2 and firmly wedges and unites it in thelengthwise slot in the backing I, making the whole practically anintegral structure. The forming dies and knurling tool are arranged inseries and series of operations are performed in a machine in which theflat strips are fed in at an end and the finished tube emerges at theother end.

The tube, due to the corrugations, is stronger" at the joint and resistsany torsional strains to which it is subjected in the use thereof, andin fact, the corrugations make the joint practically a solid rod wedgedinto the slot of the innermost tube 1.

What I claim is:

A tube construction comprising an inner tubular body slottedlongitudinally and an outer Veneer strip of a finishing metal having itsmargins" interlockedtogether in a lock seam joint consisting of layers,the joint being located in the slot and formed with internaltransversely extending corrugations exposed on the interior of the tubeleaving the outside of the tube smooth.

JOHN F. LEVAN.

